Malaria outbreak in Ethiopia linked to Asian invasive mosquito

Earlier this year malaria outbreak in Ethiopia was linked to an invasive species of mosquito that can survive the dry season, complicating efforts to keep the insects at bay.

Anopheles stephensi is a type of invasive mosquito.  Alamy Stock Photo / BSIP SA
Anopheles stephensi is a type of invasive mosquito.  Alamy Stock Photo / BSIP SA

An invasive Asian mosquito species was linked to a malaria outbreak in Ethiopia earlier this year. These insects survive even during the dry season, when other mosquitos do not have access to outdoor water sources to lay their eggs and are now invading neighboring countries.

The mosquito Anopheles gambiae is responsible for the majority of malaria infections in Africa, but Anopheles stephensi has established itself on the continent's east coast. The spread of this invasive species may complicate efforts to eliminate malaria, a mosquito-borne disease that kills approximately 670,000 people each year.

To reproduce, A. stephensi lays eggs in water and feeds on blood. This species was first identified in Djibouti in 2012, when the country was on the verge of eradicating malaria. Every year, thousands of cases are reported in the country.

The species has spread to Ethiopia, Sudan, Somalia, Yemen, and Nigeria in the last decade. According to Fitsum Tadesse of the Armauer Hansen Research Institute in Ethiopia, malaria cases in the city of Dire Dawa in eastern Ethiopia increased from 200 to 2400 in spring 2022.

"There was a significant increase in cases, but no formal investigation into what caused the increase," Tadesse says. "So we decided to jump in and look into it."

Tadesse and his team screened residents' close contacts for malaria and looked for mosquitos within a 100-metre radius of each household when they sought medical care for malaria at two local clinics in Dire Dawa. Their study lasted from April to June 2022 and included approximately 1000 participants.

Tadesse predicted that they would discover a link between the presence of A. stephensi and the city's malaria rate. A. stephensi was found in 97% of the mosquitos found by the team.

People who lived in homes with water storage containers where the insects could lay eggs were more than three times more likely to test positive for malaria than those who did not. On November 1, Tadesse presented these findings at a meeting of the American Society of Tropical Medicine and Hygiene.

A. stephensi can survive the dry season because it prefers to lay eggs in residents' water storage containers as well as outdoor water sources. "Instead of two or three months, [the malaria season] will last 12 months," says Ayman Ahmen of Sudan's University of Khartoum, who was not involved in the research. "Catastrophe is coming," says Ahmen, unless significant investment is made to prevent the spread of the insects.


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